Many firearms are designed to satisfy requirements of compactness and ergonomics during handling and storage. Several design strategies have been used to achieve compactness for shoulder-fired firearms.
Bullpup Configuration
In the traditional design of long guns, a shoulder stock is located at the rearward end of the firearm, where the “rearward end” of the firearm is the end that is placed against the user's shoulder during use. The traditional firearm further includes a receiver, trigger control, and firing mechanism located in the mid-section near the shooter's dominant hand, with a barrel extending forward from the receiver.
One design strategy used to achieve improved compactness, relative to the traditional firearm design, is a so-called “bullpup” configuration. A bullpup configuration is one in which the receiver and firing mechanism is re-located rearward with respect to the trigger control, and incorporated into the shoulder stock volume, to achieve a shorter overall length when compared to a conventional shoulder-fired firearm with a barrel of equivalent length.
In a bullpup firearm, it is typical to locate the trigger control at a conventional location and distance from the rear surface of the shoulder stock. The distance between the rear surface of the shoulder stock and the trigger control is often termed the “length of pull” of a firearm. In order to maintain a conventional length of pull in the bullpup configuration, some means is used to connect the forward-located trigger control to the rearward-located action. Typically, this is accomplished with a mechanical linkage device consisting of one or more linkage rods, linkage cables, or levers, which transmit forces from the trigger control to the firing mechanism, for example, causing a sear to release a hammer. However, these mechanical firing linkages are associated with poor ergonomic quality of the bullpup trigger control, compared to the trigger control in traditional firearm designs, because the flexing and friction of the added linkage parts contribute to additional trigger control travel, pull force (often referred to as “weight”), roughness, creep, grit, over-travel, take-up, let-off, or other common defects in ergonomic quality of trigger controls.
Takedown Configuration
Another design strategy used to achieve compactness for storage purposes is a “takedown” firearm configuration. In a takedown firearm, a forward assembly of the firearm, typically including the barrel, can be removed from a rearward assembly, typically including the stock and receiver. A takedown firearm is typified by an expedient process to assemble and disassemble the firearm, which often requires few or no tools to accomplish. Desirable aspects of a takedown firearm design include simple operation and consistency in the point-of-impact, as indicated by the firearm's sighting system point-of-aim after disassembly and reassembly operations.
In the case of takedown firearms with sighting systems mounted wholly or partially to the rearward assembly, extreme consistency of the mechanical alignment of the forward assembly must be achieved to maintain the point-of-aim indicated by the sighting system to the projectile point-of-impact. In the case of takedown firearms with sighting systems mounted wholly to the forward assembly, this extreme consistency is not required, because mechanical alignment between the sighting system and barrel bore is maintained during takedown disassembly. One patent describing a takedown firearm is U.S. Pat. No. 7,841,121. This patent describes an optical scope sighting system with a relatively long eye relief distance, which allows the rear aspect of the optical scope to be located forward of the takedown joint location. However, for scopes with typical eye relief distances, cantilevered sighting system mounts must be used to achieve acceptable eye relief distance between the ocular lens of a typical optical sighting device and the shooter's sighting eye. These cantilevered mounts protrude from the rear of the forward assembly, increasing the length of the forward assembly. This partially diminishes the main benefit of compact storage for a takedown firearm.
Stock Configuration
Still another design strategy used to achieve overall compactness is a stock that folds, telescopes, or both folds and telescopes. In the case of firearm stocks that telescope, this feature can have an added benefit of providing adjustability in the length-of-pull to best suit a particular user. Optimal length-of-pull for a particular user may vary due to arm length, neck length, sighting system, and preferred shooting posture. One patent describing a firearm with a folding and telescoping stock is U.S. Pat. No. 7,966,761. This patent describes a folding and telescoping stock which allows the firearm to be stored and manipulated more easily in confined spaces such as vehicle cabins. Extending or collapsing the telescoping adjustment on the stock allows different shooters to accommodate for differences in arm length and clothing thickness (including heavy coats or body armor) to improve the fit of the firearm.